Precontrolled 3-way pressure control valve

ABSTRACT

A precontrolled 3-way pressure control valve with a main valve having, in a valve housing, a valve bore with first, second and third control chambers connected with pressure connection, tank connection, and control connection, respectively, a control piston displaceable in a valve bore, wherein the third control chamber is connectable with the first or second control chambers, and subjectable in opposite direction to pressures from the control connection and pressure setting of a pilot valve. With deviation of pressure applied in control connection from pressure setting of the pilot valve, an imbalance of forces develops in the valve. Oblong holes, distributed over circumference of hollow control piston pass through the wall, are located in the wall radially delimiting its hollow chamber, which holes are longer than clearances between two control chambers. The hollow chamber is connected by a control nozzle on the control piston with a first pressure chamber in front of one end of the control piston, from which chamber a fluid connection leads to the pilot valve formed as a pressure-limiting valve. The control connection is connected with a second pressure chamber in front of other end of the control piston. The control piston is displaceable by pressure in the second pressure chamber against pressure in the first pressure chamber and against force of a spring arrangement by which the control piston is displaceable into position wherein the third control chamber is connected with the first control chamber, connecting the second and third control chambers.

FIELD AND BACKGROUND OF THE INVENTION

The invention is based on a precontrolled 3-way pressure control valve.

A 3-way pressure control valve of kind is known from the book "HydraulikTrainer Band 1" [Hydraulics Trainer Volume 1], published in 1991 byMannesmann Rexroth GmbH, pages 236 to 239. In this pressure controlvalve, the main piston has a piston bead by which the middle controlchamber can be sealed off from the first and second control chambers andwhich is abutted on either side by a piston neck from which controlgrooves distributed around the circumference extend into the pistonbead. The control grooves that begin at a piston neck are located at anaxial distance from the control grooves departing from the other pistonneck, said distance being approximately equal to the axial extent of themiddle control chamber.

The pilot valve of the known precontrolled pressure-regulating valve isa direct-controlled pressure-regulating valve with a pressureconnection, a tank connection, and a control connection. The controlconnection is connected with a pressure chamber in front of one end ofthe main piston by fluid. Control oil from the pressure connection ofthe main valve flows to the pressure connection of the pilot valve.Depending on the adjustment of a spring, a certain pressure is set inthe control connection of the pilot valve and hence in front of one endof the main piston. The middle control chamber of the valve bore of themain valve is connected by a housing channel with a pressure chamber infront of the other end of the main piston. In each case, a pressurebecomes established in the middle control chamber and hence in thecontrol connection such that an equilibrium exists at the main pistonbetween the various pressure and spring forces. A precontrolled 3-waypressure control valve in which the pilot valve is supplied with thecontrol oil from the pressure connection of the main valve is referredto as being high-pressure-controlled. The special advantage of this typeof precontrol consists in the main piston not tightening even with alarge volume flow and a large pressure differential between the pressureconnection and the control connection of the main valve, i.e. theconnection between the pressure connection and the control connection isinterrupted by the main piston and hence the applicability of the valveis limited. It is disadvantageous that the known precontrolled pressurecontrol valve has a tendency toward instability under certain operatingconditions, in other words pressure fluctuations occur at the controlconnection.

SUMMARY OF THE INVENTION

The object of the invention, with a valve of the above-mentioned type,is to provide precontrolled, 3-way pressure control valve that exhibitsvery stable behavior and does not tighten in response to large volumeflows with a high pressure differential between the pressure connectionand the control connection.

The 3-way pressure control valve according to the invention islow-pressure-controlled, since the control oil is supplied to the pilotvalve, designed as a pressure-limiting valve, not from the pressureconnection but from the control connection and/or from an area of thevalve in which the regulating pressure prevails. The stability of thepressure-control valve is considerably improved by this type of controloil removal and by the type of pilot valve.

For a general understanding of a precontrolled 3-way pressure controlvalve it is sufficient to assume that in all the chambers of the valveopenly connected with the control connection, the same static pressureprevails, namely the control pressure. On closer examination, however,it becomes evident that there are local deviations from the controlpressure everywhere, caused by the geometry of the main piston and thehollow chambers in the valve housing, and that therefore the geometryand the point at which the control oil flowing to the pilot valve isremoved influence the function of the pressure control valve. In aprecontrolled 3-way pressure control valve according to the invention,it is now possible, as a result of the special nature of the main pistonand by the way in which control oil is supplied from the controlpressure area, into the first pressure chamber located in front of oneend of the main piston, which can also be referred to as the controlpiston, to avoid tightening of the valve even with high-volume flows andhigh pressure differentials between the pressure connection and thecontrol connection.

An advantageous embodiment is the control piston with regard to thehollow chamber in it and in regard to the oblong holes that form aconnection between the outer circumference of the control piston and thehollow chamber. Other features of the invention relate primarily to theway in which the two pressure chambers in front of the ends of thecontrol piston are connected with the control connection and with thepilot valve.

In conjunction with the formation of the oblong holes, it has proven tobe especially advantageous where the oblong holes are shorter than theclearance between the first control chamber and the second controlchamber and where a precision control pocket that is closed radiallyinwardly axially adjoins each oblong hole on one side, with the totallength of a portion of the control piston containing an oblong hole andat least one precision control pocket being approximately equal to theclearance between the first control chamber and the second controlchamber. Preferably the total length of the portion is slightly greaterthan the clearance between the two control chambers mentioned above. Thetransient response of the pressure control valve during changes in theguide valve, in other words the control pressure setpoint, is influencedpositively by the precision control pocket. The control pressuresetpoint is specified by the setting of the pilot valve. If this valveis a pressure-limiting valve that can be controlled proportionately, forexample with the aid of an electromagnet, the control pressure setpointcan be changed rapidly. If the total length of the oblong hole and theprecision control pocket is slightly greater than the clearance betweenthe first control chamber and the second control chamber, one speaks ofa negative overlap of the control edges on the control piston and on thefirst and second control chambers. In one position of the control pistonin which no significant volume flow from either the pressure connectionto the control connection or from the control connection to the tankconnection is present, a leaking oil stream constantly flows from thecontrol connection to the tank connection which must be compensated bythe pressure connection. However, undesired periodic pressurefluctuations in the control connection are then avoided by the negativeoverlap of the control edges.

Preferably, a precision control pocket adjoins each oblong hole axiallyon both sides. It is basically possible to design the two precisioncontrol pockets differently at an oblong hole with regard to theirlength, depth, or their width. Preferably however the two precisioncontrol pockets on either side of an oblong hole are of equal size.

According to the invention, the control oil flows to the first pressurechamber from the hollow chamber of the control piston through aninternal fluid connection in the control piston. Preferably, theconnection of the control connection is linked with the second pressurechamber in front of the other end of the control piston, from the hollowchamber of the control piston takes place through the control piston.

With an arrangement of damping nozzles in accordance with a feature ofthe invention, the behavior of the valve can be influenced. Inparticular, a nozzle between the second pressure chamber and the firstpressure chamber or the pilot valve has a favorable effect on thetransient response of the pressure control valve.

An embodiment of a precontrolled 3-way pressure control valve accordingto the invention as well as two types of precontrol are shown in thedrawings. The invention will now be described in greater detail withreference to the figures of these drawings.

It shows:

FIG. 1 a partial lengthwise section through the embodiment with a firsttype of precontrol,

FIG. 2 an enlarged portion of FIG. 1 with a slightly different positionof the control piston,

FIG. 3 is a top view of the control piston as viewed in the direction ofarrow A in FIG. 2,

FIG. 4 a section along line IV--IV in FIG. 2 and

FIG. 5 a schematic view of a second type of precontrol.

The precontrolled 3-way pressure control valve according to FIG. 1 has athrough valve bore 11 in a valve housing 10 of its main valve 9, inwhich bore a main piston 12 is axially displaceable as a control piston.Valve bore 11 is sealed on both sides by covers 13 that are screwed tothe valve housing 10 and have a recess 14 with a central elevation 15 inextension of the valve bore.

Valve bore 11, at several places that are spaced axially from oneanother, is widened into control chambers in the form of annularchannels. A first control chamber 16 is located in the center of valvebore 11 and is connected with a pressure connection P of the main valve9. At a greater distance from the first control chamber 16 there are twosecond control chambers 17 connected with one another by a bridgechannel 18 and also with a tank connection T of the main valve 9.Between the control chamber 16 and each control chamber 17, a thirdcontrol chamber 19 is located, of which only one is used as a controlconnection A of the valve. The other control chamber 19 is sealed offfrom the outside. In addition, only one of the two control chambers 17is used, namely the one which, as viewed from the first control chamber16, is located beyond the third control chamber 19 that is used. The twosuperfluous control chambers 17 and 19 are present because, for costreasons, the same valve housing is used as for the precontrolled 4/3-wayvalves that are manufactured in large numbers. When reference is made inthe following to a control chamber, this is to be understood to mean acontrol chamber that is used.

Sharp control edges 22 and 23 are formed, at least on control chamber 16and on control chamber 17, by undercuts 20 and 21 on the axial lateralsurfaces that face away from one another, the edges being located at apredetermined distance from one another.

Control piston 12 comprises essentially three parts, namely a tube 27 aswell as two sealing pieces 28 that are screwed inward from the two endsof tube 27 until they contact a flange 29 on the respective end of tube27. Viewed as a whole, control piston 12 is therefore a hollow pistonwith a hollow chamber 30 that extends axially between the two sealingpieces 28. The ratio between the diameter of hollow chamber 30 and theoutside diameter of control piston 12 is approximately 0.75. A coilcompression spring 31 is located between the flange 29 of one sealingpiece 28 and one cover 13, the spring urging the control piston againstthe other cover 13.

Hollow chamber 30 is open to the outside of the control piston 12through four oblong holes 32 that extend in the axial direction, theholes being distributed at equal angle intervals around thecircumference of the control piston. The oblong holes 32 terminateaxially in an arc with a radius that has half the width of an oblonghole. Oblong holes 32 are shorter than the distance between the controledges 22 and 23 and longer than the spacing at the center between thetwo control chambers 16 and 19. They are in an area of control piston 12such that when the control piston, as seen in FIG. 1, abuts theright-hand cover 13, the control chambers 16 overlap axiallyapproximately halfway and the control chambers 19 overlap completely.Hollow chamber 30 is much longer than the oblong holes 32 and extends onboth sides far beyond oblong holes 32.

On both sides, each oblong hole is adjoined in the axial direction by afine control pocket 33, which is delimited radially internally by aplane bottom 34. The two fine control pockets 33 on either side of anoblong hole 32 are made identical to one another. They have the sameradial depth, the same width, namely the width of oblong hole 32, andare delimited axially by an arc whose radius is equal to half the widthof the oblong hole and the fine control pockets. The length of each finecontrol pocket 33 is only a sixth to a seventh of the length of anoblong hole 32. The total length of an oblong hole 32 and the two finecontrol pockets 33 associated with an oblong hole is slightly greaterthan the distance between the two control edges 22 and 23. Between thesecontrol edges on valve housing 10 and oblong holes 32 including the finecontrol pockets 33, there is therefore a negative overlap. This isevident in particular from FIGS. 2 and 3 in which oblong holes 32 assumea central position relative to control edges 22 and 23 of valve housing10, in which an opening cross section designated by S and shadedhorizontally in FIG. 3 exists between the fine control pockets 33 andcontrol edges 22 and 23.

The two sealing pieces 28 are traversed centrally by an axial bore 40whose diameter is much smaller than the diameter of hollow chamber 30. Afirst pressure chamber 42 that is located in front of the end of controlpiston 12 that is subjected to the action of coil compression spring 31is fluidly connected with hollow chamber 30 by axial bore 40 in onesealing piece 28 and by a replaceable control nozzle 41, which islocated in the axial bore at a distance from hollow chamber 30. By meansof cast and drilled channels 43 and 44 in valve housing 10, there is afluid connection from pressure chamber 42 to the pilot valve 45 designedas a proportional pressure-limiting valve. A damping nozzle 46 is alsolocated in the fluid connection, but is not required for the basicfunction of the pressure-regulating valve. The setting of the pilotvalve 45 can be changed by a proportional electromagnet 47. Depending onthe level of the current flowing through electromagnet 47, pilot valve45 opens when there is a different pressure at its input.

A second pressure chamber 48 that is located from the other end ofcontrol piston 12 is connected with hollow chamber 30 through axial bore40 of the other sealing piece 28, with it being possible to provide apreferably replaceable damping nozzle 49 in this connection. There is noneed as such for additional connections to second pressure chamber 48.In the embodiment according to FIG. 1, however, the second pressurechamber 48 is connected by channels that correspond to channels 43 and44 and a damping nozzle 50 located therein with the first pressurechamber 42.

In the alternative precontrol according to FIG. 5, the pressure-limitingvalve 45 can be adjusted manually to various values. Damping nozzle 50is not located between the second pressure chamber and the firstpressure chamber, but between the second pressure chamber and pilotvalve 45.

In the normal design of a precontrolled 3-way pressure control valveaccording to the invention, two nozzles 41 and 46 are used that have thesame opening cross section. The connection between hollow chamber 30 andsecond pressure chamber 48 is open, in other words nozzle 49 is notinserted. The connection between the second pressure chamber 48 and thefirst pressure chamber or the pilot valve is closed by a plug.

With the aid of the 3-way pressure control valve shown, a pressure thatcan be predetermined by the setting of the pilot valve is maintained incontrol connection A. In this way, a distinction is made between apressure-reducing function in which, to maintain the pressure in controlc-connection A, pressure medium from pressure connection P must besupplied to the control connection A and a pressure-limiting function inwhich, to maintain the pressure in control connection A, pressure mediummust flow out of connection A to tank connection T, and apressure-maintaining function in which the volume flow is essentiallyzero and only a volume flow of leaking oil is replaced.

In an initial position of the valve, control piston 12 is pressed bycompression spring 31 against one cover 13. The connection betweencontrol chambers 16 and 19, in other words between pressure connection Pand control connection A, is fully open. When a volume flow is flowingfrom pressure connection P to control connection A, this flow builds upa pressure in control connection A. This pressure acts through oblongholes 32, hollow chamber 30, and axial bore 40 in one sealing piece 28and the control nozzle 41 in the first pressure chamber 42 and throughthe other sealing piece 28 in second pressure chamber 48 as well. Themaximum opening cross section between pressure connection P and controlconnection A remains initially until the pressure in control connectionA reaches the value set on pilot valve 45. Pilot valve 45 opens and acontrol volume flow begins to flow to the tank from hollow chamber 30through control nozzle 41, first pressure chamber 42, channels 43 and44, as well as damping nozzle 46 and the open control cross section ofthe pressure-limiting valve 45. When the control volume flow is so greatthat the critical pressure drop at control nozzle 41 that corresponds tothe pretensioning force of compression spring 31 based on thecross-sectional area of control piston 12 subjected to the pressure isexceeded at approximately 2 bars for example, control piston 12, as seenin FIG. 1, moves to the left and throttles the connection from pressureconnection P to control connection A until a new equilibrium of forcesis established at control piston 12. The pressure determined by thesetting of pilot valve 45 in control connection A is largely independentof the volume flow from P to A and is maintained largely independentlyof the pressure level in P. Of course it is assumed that the pressuredifferential between P and A is at least as great as the through-flowresistance of the valve for the volume flow in question.

If the pressure in A, under the influence of external forces, forexample on a cylinder, exceeds the value set by pilot valve 45, thispressure acts in the second pressure chamber 48 and displaces controlpiston 12 to the point where the connection from A to T at control edge23 and the corresponding precision control edges is opened. Then,largely independently of the volume flow from A to T, the pressure in Ais kept constant to correspond to the value set on pilot valve 45.Connection P is blocked in the course of this pressure-limiting functionof the valve.

When no volume flow is required in connection A, for example when ahydraulic cylinder or a hydraulic motor is at rest, the valve operatesin a pressure maintenance function. Control piston 12 is displaced fromits starting position sufficiently far to the left that the controlcross section at control edge 22 of valve housing 10 remains open onlyso far that the control oil volume flow required for pressure regulationis maintained, possible leaking oil losses in A are compensated, and aleaking oil flow from A to T that may be present because of the negativeoverlap is replaced.

What is claimed is:
 1. Precontrolled 3-way pressure control valve with adirectly controlled pressure valve (45) as a pilot valve, with a mainvalve (9) that has, in a valve housing (10), a valve bore (11) with afirst control chamber (16) connected with a pressure connection (P),with a second control chamber (17) connected with a tank connection (T),and with a third central control chamber (19) connected with a controlconnection (A) as well as a control piston (12) displaceable in valvebore (11), by which the third control chamber (19) can be connected withthe first control chamber (16) or with the second control chamber (17),and can be subjected in the opposite direction to the pressures that arederived from the pressure in control connection (A) and from thepressure setting of pilot valve so that, with a deviation of thepressure applied in control connection (A) from the control pressurespecified by the pressure setting of the pilot valve (45), an imbalanceof forces develops in said valve, wherein the control piston (12) isformed as a hollow piston with a hollow chamber (30), a plurality ofoblong holes (32) that are distributed over the circumference of thecontrol piston (12), pass through the wall, and run axially, are locatedin the wall that radially delimits the hollow chamber (30), which holesbeing longer than the clearances between two control chambers (16, 19;17, 19), the hollow chamber (30) of the control piston (12) is connectedby a control nozzle (41) on control piston (12) with a first pressurechamber (42) that is located in front of one end of control piston (12),from which chamber a fluid connection leads to the pilot valve that isformed as a pressure-limiting valve (45), the control connection (A) isconnected with a second pressure chamber (48) located in front of theother end of the control piston (12), and the control piston (12) isdisplaceable by the pressure in the second pressure chamber (48) againstthe pressure in the first pressure chamber (42) and against the force ofa spring arrangement (31) by which the control piston (12) can bedisplaced into a position in which the third control chamber (19) isconnected with the first control chamber (16), connecting the thirdcontrol chamber (19) with the second control chamber (17). 2.Precontrolled 3-way pressure control valve according to claim 1, whereinthe hollow chamber (30) is substantially longer on both sides thanoblong holes (32).
 3. Precontrolled 3-way pressure control valveaccording to claim 1, wherein the ratio between the diameter of thehollow chamber (30) and the outside diameter of the control piston (12)is between 0.7 and 0.8.
 4. Precontrolled 3-way pressure control valveaccording to claim 1, wherein the length of an oblong hole (32) is atleast as great as the central spacing between two control chambers (16,19; 17, 19).
 5. Precontrolled 3-way pressure control valve according toclaim 1, wherein the length of oblong holes (32) is less than theclearance between the first control chamber (16) and the second controlchamber (17), a radially internally closed fine control pocket (33)axially adjoins each oblong hole (32) at least on one side, and thetotal length of a portion of the control piston (12) that has an oblonghole (32) and at least one fine control pocket (33) is approximatelyequal to the clearance between the first control chamber (16) and thesecond control chamber (17).
 6. Precontrolled 3-way pressure controlvalve according to claim 5, wherein a fine control pocket (33) adjoiningan oblong hole (32) has the same width as the oblong hole (32). 7.Precontrolled 3-way pressure control valve according to claim 5, whereina fine control pocket (33) closes with an arc whose radius is equal tohalf the width of the fine control pocket (33).
 8. Precontrolled 3-waypressure control valve according to claim 5, wherein a fine controlpocket (33) adjoins each oblong hole (32) axially on both sides. 9.Precontrolled 3-way pressure control valve according to claim 8, whereinthe two fine control pockets (33) on both sides of an oblong hole (32)are the same.
 10. Precontrolled 3-way pressure control valve accordingto claim 9, wherein an oblong hole (32) is approximately six to seventimes as long as a fine control pocket (33).
 11. Precontrolled 3-waypressure control valve according to claim 8, wherein the two finecontrol pockets (33) on both sides of an oblong hole (32) differ fromone another.
 12. Precontrolled 3-way pressure control valve according toclaim 1, wherein an axial bore (40) with a diameter smaller than that ofthe hollow chamber (30) runs between the control nozzle (41) and thehollow chamber (30).
 13. Precontrolled 3-way pressure control valveaccording to claim 1, wherein the connection of the control connection(A) with the second pressure chamber (48) from the hollow chamber (30)of control piston (12) occurs through the control piston (12). 14.Precontrolled 3-way pressure control valve according to claim 13,wherein an axial bore (40) runs from hollow chamber (30) in thedirection of second pressure chamber (48) and is narrower than hollowchamber (30).
 15. Precontrolled 3-way pressure control valve accordingto claim 1, wherein a damping nozzle (49) is connected in front of thesecond pressure chamber (48) toward the control connection (A). 16.Precontrolled 3-way pressure control valve according to claim 1, whereinthe first pressure chamber (42) is connected fluidly with the pilotvalve (45) by a damping nozzle (46).
 17. Precontrolled 3-way pressurecontrol valve according to claim 1, wherein the second pressure chamber(48) is connected by a damping nozzle (50) with the first pressurechamber (42) or with the pilot valve (45).
 18. Precontrolled 3-waypressure control valve according to claim 1, whereinthe length of anoblong hole (32) is at least as great as the central spacing between twocontrol chambers (16, 19, 17, 19), and the length of oblong holes (32)is less than the clearance between the first control chamber (16) andthe second control chamber (17), a radially internally closed finecontrol pocket (33) axially adjoins each oblong hole (32) on both sides,and the total length of a portion of the control piston (12) that has anoblong hole (32) and two fine control pockets (33) is approximatelyequal to the clearance between the first control chamber (16) and thesecond control chamber (17).
 19. Precontrolled 3-way pressure controlvalve according to claim 18, wherein a fine control pocket (33)adjoining an oblong hole (32) has the same width as the oblong hole(32).
 20. Precontrolled 3-way pressure control valve according to claim19, wherein a fine control pocket (33) closes with an arc whose radiusis equal to half the width of the fine control pocket (33).